The present disclosure relates to a semiconductor component and to a corresponding production method.
Although applicable to any semiconductor components, the present disclosure and the problem which it is intended to solve will be explained with reference to a micromechanical pressure sensor.
DE 10 2006 026 881 A1 discloses a mounting concept for an absolute pressure sensor in open cavity full mold technology. In this mounting concept, a chip is fastened on a lead frame, wire-bonded and injection molded around with a molding compound in such a way that the sensor chip partly protrudes from the molding compound. The sensor membrane lies in the part around which injection molding is not carried out.
Conventionally, micromechanical sensor devices are packaged in molded housings made of plastic. On the one hand, so-called leaded housings are used in this case, which comprise curved contact feet for contacting the next plane and fully encapsulate the chip or chips. On the other hand, there are so-called overmolded leadless housings, which are distinguished by the lack of contact limbs. The contacting of the next plane is in this case carried out via contact surfaces on the lower side of the package. The basic system of these molded package variants generally consists of a substrate (Cu, FR4), an adhesive, the silicon chip or chips and the molding compound.
Another package variant consists of expensive premold housings. These are prefabricated injection-molded base housings which are closed with a cover after positioning and contacting of the semiconductor chips. The premold housings constitute a low-stress form of package since there is no direct contact between the assembly partners silicon and molding compound. Furthermore, the cavity existing inside the package, together with an opening in the package, are advantageous and expedient for the media accesses, such as are required for example for pressure sensors, IR sensors and microphones.
With respect to the cost aspect, attempts have been made to produce media accesses and cavities in full mold packages (fully encapsulated) as well. In a first concept, the so-called film mold method is used. In this case, the media access is produced by means of the shape of the molding tool. A projecting tool structure is placed directly on the semiconductor chip and prevents overmolding in this region, for example in the region of a pressure sensor membrane. For tolerance compensation, the molding tool is coated with an ETFE film (ETFE=ethylene-tetrafluoroethylene). The latter is highly deformable and lies geometrically accurately over the tool surface. In this method, there is a direct dependency between the sensor layout and the tool structures. The tool must cover the active membrane structures, but without covering pad surfaces or wire bonds. It is therefore necessary to comply with certain design rules. Furthermore, depending on the layout, full placement of the tool on the active structures, for example membranes, may also be necessary and lead to mechanical stresses. With this method, it is not possible to produce undercuts in the cavities.
Another concept is based on the use of a laminate-based substrate in conjunction with contacting by means of flipchip and underfill technology. The mechanical and electrical contact of the sensor with the substrate is in this case established by solder balls or studbumps and an underfill. The pressure sensor membrane remains uncovered and receives the media access through an opening in the substrate. Above all, however, the point of the underfill proves critical. In order not to cover the membrane with the underfill, the breaking capillary effect on the edge of a substrate opening is employed. The size and edge shape of the opening are therefore indirectly coupled with the flow path of the underfill (and vice versa) and therefore the function of the sensor membrane. Furthermore, the underfill in the meniscus formed is drawn toward the membrane and therefore takes up unused sensor surface area.
FIGS. 9a,b are cross-sectional views of an exemplary semiconductor component in the form of a micromechanical pressure sensor arrangement, FIG. 9b representing a detail enlargement of the region A of FIG. 9.
In FIGS. 9a,b, reference SUB denotes a circuit board substrate, onto which an analysis chip 3 and a micromechanical pressure sensor chip 5 are applied by means of solder balls LK. Underneath the micromechanical pressure sensor chip 5, an underfill U is provided, which serves for mechanical stabilization. The two chips 3, 5 are packed in a molded package 8 consisting of molding compound or pressing compound. The membrane region M of the pressure sensor chip 5 is kept free of underfill U, because an opening L is provided in the substrate at the corresponding position. As can be seen from FIG. 9b, the underfill U forms a meniscus MIN between the edge on the opening L and the micromechanical pressure sensor chip 5, which leads to an increased space requirement.